For many different processes it is of great importance to know the magnitude of the surface tension of a liquid. The surface tension can indicate the substances present in the liquid and the concentration of known and unknown substances. By continuously measuring the surface tension, dynamically or statically, possibilities of analyzing a liquid are provided. The analysis can then for example be used to control the concentration of different substances in the liquid.
A problem existing today is that it is not possible to continuously measure surface tension in a dynamic and accurate way. The conventionally used methods of measuring surface tension are based on an external analysis of the surface tension, i.e. that a sample must be taken from the system in order that it will be possible to then make an analysis thereof. These methods result in a long time period before a response can be obtained. Of course, the drawbacks of such methods are plural, including the following ones:                Used time: Due to the fact that the measurement can not be made in the process it takes a longer time.        No possibility of immediately obtaining a response. It means that in many cases one has to wait for up to one week for a response to the question whether for example a correct tenside concentration exists in a process bath. In some cases the producing company must place the product which has already been produced in quarantine waiting for the result of the analysis. In the case of a negative response all of the already produced material must be reprocessed or in a worst case totally discarded.        Requirement of manual work. Today manual work is required when using all existing methods.        No possibility of dynamic feedback. Since it is not possible to dynamically control these processes in a feedback manner any possibility of continuously controlling the contained amounts of different substances in the process is lost.        
In the article Nels A. Olson, Robert E. Synovec, William B. Bond, Dana M. Alloway, Kristen Skogeboe, “Dynamic Surface Tension and Adhesion Detection for the Rapid Analysis of Surfactants in Flowing Aqueous Liquids”, Anal. Chem. 1987, Vol. 69, pp. 3496-3505 a method of measuring surface tension is described. Drops are, by a liquid flow through a capillary, formed at the end of the capillary in contact with the ambient air and the pressure the liquid is measured during the formation and the detaching of the drops from the end of the capillary. The pressure is measured by a differential pressure sensor connected both to the capillary and to the surrounding air. Disadvantages are associated with this method. For example, a temperature difference between the drops and the ambient air or gas can exist that can cause precipitation of salts which clogs the capillary.
Similar methods of measuring surface tension are described in the articles C. A. MacLeod, C. J. Radke, “A Growing Drop Technique for Measuring Dynamic Interfacial Tension”, Journal of Colloid and Interface Science, 1993, Vol. 160, pp. 435-448, and Keith E. Miller, Emilia Bramanti, Bryan J. Prazen, Marina Prezhdo, Kristen J. Skogerboe, Robert E. Synovec, “Multidimensional Analysis of Poly(ethylen glycols) by Size Exclusion Chromotography and Dynamic Surface Tension Detection”, Anal. Chem., 2000, Vol. 72, pp. 4372-4380.